Evaluation of CO₂ flooing in Multi-layered heterogeneous reservoir

Abstract

Carbon dioxide (CO₂) miscible flooding is widely performed to improve oil recovery. This technique recovers oil through miscibility mechanism between CO₂ and reservoir fluid. Since CO₂ is less dense compared to reservoir oil, this leads to gas overriding and instability of flood front, resulting in poor recovery efficiency. This study aims to investigate effect of uncontrollable parameters consisting reservoir heterogeneity, formation depositional sequence and dip angle. Appropriate conditions combined with controllable parameters including CO₂ injection rate and CO₂ injection perforation interval are also studied. ECLIPSE®300 reservoir simulator is utilized. Each heterogeneous reservoir model is constructed by varying permeability in each layer and it is assigned with Lorenz coefficient (Lc). Results indicate that pre-flushed water is required and 0.2 PV is found to be optimum. About 68% of oil recovery is achieved from this CO₂ flooding base case, where 8% is higher than just solely waterflood. Although, miscible bank can extract intermediate hydrocarbon, without pressure support from injected water, oil production can be terminated early. The results also show that, with a big slug of water arrival to production well at late period, production can be prolonged due to a bounce of oil rate above well shut-in limit. Reservoir heterogeneity plays a role, affecting stability of flood front and also recovery performance.